The invention relates to a thread supply device for textile machines, in particular knitting machines, comprising a stationary thread drum onto which a thread which comes from a storage bobbin can be wound tangentially by means of a wnding-on member rotating around the drum edge for forming an intermediate thread supply and from which the thread can be pulled downwardly through a central withdrawal eye, and further comprising a thread control element arranged in the area of the withdrawal path of the thread and having the form of a hook secured on the winding-on member, which hook receives the unwinding thread in its hook mouth and through this limits the withdrawal speed to the winding-on speed.
The basic purpose of the invention is to further develop a thread supply device of the above-described type so that it permits an indication of an undesired strong drop of the withdrawal tension.
This purpose is attained according to the invention by providing a cut-off eye in the thread path downstream of the hook, which eye is arranged on a swivel arm which can be swung transversely relative to the thread path from an operating position into a nonuse or shut-off position, and which arm is hinged to the rotating winding-on member and the swivel axis of which coincides with the axis of the thread drum.
The invention takes advantage of the following situation: in a thread supply device of the described type, the thread which is withdrawn downwardly from the thread drum during a positive thread delivery operation laterally rests against a thread control element, such as a hook. This lateral engagement of the thread on the thread control element is created because the withdrawn thread tries to run around the thread drum due to the withdrawal tension of the thread. However, this movement of the withdrawal thread is prevented by the thread control element. Thus, only as much thread can be withdrawn as is released by the rotation of the thread control element, which thread control element rotates together with the winding-on member around the thread drum. In this manner, the point at which the thread is withdrawn downwardly from the thread drum rotates at the same speed as the winding-on member or as the thread control element. If the tension in the withdrawn thread drops, then less thread is withdrawn from the thread drum than is released based on the rotation of the thread control element. Since the thread control element rotates together with the winding-on member at an unchanged speed, the withdrawn thread will trail or fall behind the thread control element, or may even stop at one point (in the case of an extremely strong drop in the withdrawal tension). Under these conditions, the withdrawal thread will retard the swivel arm of the cut-off eye in its rotation, which swivel arm usually rotates uniformly with the thread control element, and will thus swing the cut-off eye from its operating position into the nonuse or shut-off position. Thus, the swivelling of the cut-off eye and of the swivel arm can be utilized to indicate a decrease in the thread withdrawal tension or to stop the respectively supplied textile machine.